The present invention relates to a method of cleaning grain.
Before grain can be converted to whole-grain products or to bran for dietetic purposes, it must be cleaned to the maximum possible extent, particularly on its surface including in the crease which is present in each kernel of grain. Such cleaning is also desirable if flour is to be produced from grain under conditions which involve a high degree of milling. None of the known and heretofore practiced methods meet this requirement even remotely, in part because the rill in the grain is deep and almost closed, and in part because there are many different types of contaminants to be removed and these different types have different physical characteristics.
The contamination of the grain surface basically consists of mechanical dirt which is impregnated with various fat and water soluble substances so that it often forms solid encrustations which are difficult to remove and which cannot even be completely removed from the free surface by washing with water, so that certainly the dirt or contamination present in the deep crease remains almost completely untouched by the washing process.
This dirt often contains residues of deleterious chemicals, such as weed killers, pesticides, heavy metals such as lead, quicksilver or cadmium, radio-nucleides and strontium, cesium or tritium and carcinogens such as for example benzopyrene. Because a part of these deleterious substances enters into two outer layers of the pericarp; because mold hyphae firmly grow into the hypodermis and because the empty spaces between the cells of the hypodermis are filled with bacteria, it is advantageous to also remove the loose surface layers i.e. epidermis and the hypodermis when the surface of the grain is being cleaned. This must take into account that the cuticula of the grain consists of several layers, namely the outer pericarp or epidermis, the elongate cell layer or hypodermis located beneath it, and the cross cell layer located beneath the hypodermis, and finally a fourth tube-cell layer which is the innermost one. The pericarp (fruit-coat) composed of the four aforementioned layers surrounds the seed coat which, together with the aleuron layer beneath it, in turn surrounds the starchy endosperm. The pericarp composed of the four layers has, in the case of wheat, a weight percentage of approximately 4.4% and in the case of rye of approximately 6.3% of the total weight of the grain. The two layers of the pericarp which are to be removed have, in both instances, a weight percentage of approximately 3.5 of the total weight of the grain.
The removal of the two outer layers of the pericarp (epidermes+hypodermis) cannot be effected with the known methods. Dry peeling is not very effective. Wet peeling is in many instances undesirable because the smeary substances which form with the wet dust constitute a most suitable substrate for microorganisms which grow rapidly and contaminate not only the partially peeled grain but also the equipment for treating and conveying it. Also, in the heretofore practiced and known wet peeling methods, the crease in the grain is practically untouched.
Chemical peeling methods should inherently be more effective than those mentioned above, but cannot be used because the chemicals which are required are forbidden by the Pure Food Laws and also in many instances have a disadvantageous effect upon formation of flour during the milling of the grain or upon the baking characteristics of flour so produced.
Also to be removed, and to be removed completely, is the filth which is in part regularly composed of insect particles and insect eggs, such as grain borers, flour moths and mites. These eggs cannot be removed during washing because they are located in the crease where they can rapidly develop in the event of advantageous ambient conditions.